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Researching the Fortress of Louisbourg National Historic Site of Canada
  Recherche sur la Forteresse-de-Louisbourg Lieu historique national du Canada

DOMESTIC BUILDING CONSTRUCTION 
AT THE FORTRESS OF LOUISBOURG, 1713 - 1758

By

Eric Krause

1996 Draft Report

(Fortress of Louisbourg
Report Number H G 10)

CHAPTER SEVEN

ROOFS - ROOF STRUCTURES

The design of a roof, usually hipped or gabled, depended upon personal preference, price, aesthetics or tradition. The Custom of Paris, Louisbourg's civil code, could also colour design on occasion. A builder, wishing to place an attic window in an end wall, for example, could always do so by raising a gabled roof, but if the wall straddled a property line, he would have to adhere to Articles 199-202 of the Custom - articles which could restrict the window to a precise location while adding to its cost. Otherwise, he could reach an agreement with his neighbour to waive these building restrictions, not place a window at all, or raise a hipped roof with a dormer instead.

A dormer, unlike a window, did not usually provide a view within the meaning of Articles 199-202, since it did not normally allow a person "to look perpendicularly into the home of a neighbour." Unfortunately, a hipped roof created a problem which a gable avoided: it caused water to flow, and if that flow were upon a neighbour's property or building, a legal entanglement was always a possibility. In Louisbourg, as in France, roof gutters were a solution; the neighbour waiving his rights, either in writing or verbally, was another solution; or the builder might decide against a hip roof, and look to another design instead.

A mansard style roof was generally not popular in Louisbourg, although the military proposed this kind of design for several early barrack buildings, including that of the King's Bastion. There were probably no more than three buildings in Louisbourg with a mansard roof, each on private lots, in Blocks 4, 16 and 34.

The only other known roof structures of Isle Royale were the shed, the flat and the pyramid types. They were generally associated with secondary buildings, such as lean-tos and latrines.

Roof structures at Louisbourg, whether hipped or gabled, with either tied rafters, trussed rafters, or a trussed system of purlins carrying rafters, represented the range of choices builders had from the most simple system, being the use of common rafters only, to the most complex, being the truss. Typically, a truss consisted of one king post, two principal rafters, one collar beam, and two braces. In addition, there could be a cross beam running from one wall to another to replace or join a collar beam, or other secondary bracing and purlins in support of the roof.

Roof structures in Louisbourg were not unlike those of other towns of Europe and North America. Yet they were typically French. They usually had ridge beams, king posts and flared eaves, produced by a timber, generally 3 pieds long, attached to the ends of the rafters, to throw water clear of the walls.

The ridge beam at Louisbourg was usually beveled on top and on two sides to allow the other members to fit cleanly, usually passing over the king post. On occasion, however, it was framed into the king post instead as, for instance, one was described in a 1750 building contact for a large military latrine.

Ridge beams were not mandatory, however. A 1752 contract and plan for a large brewery, its single-pitched main roof sloping off a high, masonry wall, specified 14 trusses in all; but no ridge beam.

Builders wishing to transfer the weight of a roof to a perimeter wall generally, though not always, used a wooden plate, either single or double, between the wall - be it masonry, charpente or piquet - and the roof members. Walls of masonry structures were usually of sufficient width to require not only a double plate but also blockers in some cases, placed in the empty cavity that could result between plates.

Interior bearing walls appear not to have been common in Louisbourg, but were sometimes required to aid perimeter walls in support of a roof structure. In 1723 a Royal Battery proposal stressed that the number of interior walls depended on the number of roof trusses, thereby sustaining the ridge beam, and the purlins at 6 pieds intervals.

Roofing members were often on the large side and, being timberwork, were usually hand-hewn rather than sawn. Sawn members were used, however, particularly in less refined structures, two boards, for example, comprising the ridge of an inexpensive Barrachois house. In some piquet buildings, half-squared off members and in the round (poles) were even tried. Piquet trusses and rafters were also fairly common.

Roof timbers - pine or red pine of Isle Saint Jean are mentioned - varied in size according to use: the smallest being 3 by 3 pouces for the accoyeau of a flared eave, to 11 by 12 pouces for a hip rafter. In between there was a large variety of sizes that were used.

Builders would have preferred to flash with sheet lead but lead was extremely expensive. Consequently, they probably more often caulked ridges and valleys with mortar or plaster, particularly since these were the usual materials for flashing chimney stacks and dormers.

Finally, a few roofs had gutters, most likely inexpensive wooden gutters, like the 4 by 4 pouce timber ones of the Vallée masonry residence; some having been placed to satisfy the terms of the Custom of Paris, others for more practical rather than legal requirements. More expensive gutters, like the lead gutters of the barracks of the King's Bastion, would not have been popular with private builders however.